1. Field of the Invention
The invention relates generally to an improved reactor for pyrolysis of solid particulate biomass material, and more particularly to the mixing zones for mixing the solid biomass materials with a lifting medium and with a heat transfer medium.
2. Description of the Related Art
Entrained bed reactors, also referred to as transport reactors, are well known in the field of fluid catalytic cracking (FCC). This process is employed in crude oil refineries for cracking relatively heavy feedstocks, such as vacuum gas oil (VGO) to hydrocarbon compounds having boiling points in, for example, the gasoline and diesel ranges.
In a typical FCC reactor, hot particulate catalyst is mixed in a mixing section with a non-oxidizing lift gas. The hot catalyst particles become entrained by the flow of lift gas. The liquid feedstock is sprayed into this flow of entrained catalyst particles. Upon contact with the heat of the catalyst particles, the feedstock droplets rapidly vaporize. The formation of feedstock vapors causes a further acceleration of the catalyst particles. The hydrocarbons present in the vapors are catalytically cracked to the desired molecular weight range.
U.S. Pat. No. 5,961,786 to Freel et al. discloses an FCC-type reactor for carrying out a thermal or catalytic pyrolysis of a variety of feedstocks, including liquid and solid biomass materials. The reactor is an upflow, entrained bed reactor, and comprises a mixing section with a first inlet means and a secondary inlet means. Hot transfer medium particles are introduced into the mixing zone via the first inlet means. The lifting gas takes up the heat transfer particles and carries them upward. Feedstock is injected into the flow of hot heat transfer particles via the secondary inlet means.
The '786 patent contains examples on use of the reactor in the pyrolysis of wood particles, using sand as the heat transfer medium. The stated aim is to produce wood distillation products that can be used as “liquid smoke” products for flavoring food products, such as meats. The wood distillation products are characterized by a low pH (around 3.0) and a high oxygen content, making them unsuitable for use as liquid fuels or as a blending stock for liquid fuels.
There is a need for an entrained bed reactor for the pyrolysis of solid biomass materials to a liquid product having a low oxygen content.
Thus, there is a particular need for an entrained bed reactor for use in a catalytic pyrolysis process for solid biomass materials.